**EXHIBIT 31.1**

**CERTIFICATION**

I, David J. Mazzo, President and Chief ExecutiveOfficer of Æterna Zentaris Inc., certify that:

1.               I have reviewedthis amended annual report on Form 40-F of Æterna Zentaris Inc;

2.               Based on myknowledge, this report does not contain any untrue statement of a material factor omit to state a material fact necessary to make the statements made, inlight of the circumstances under which such statements were made, notmisleading with respect to the period covered by this report;

3.               Based on myknowledge, the financial statements, and other financial information includedin this report, fairly present in all material respects the financialcondition, results of operations and cash flows of the issuer as of, and for,the periods presented in this report;

4.               The issuer’s othercertifying officer and I are responsible for establishing and maintainingdisclosure controls and procedures (as defined in Exchange ActRules 13a-15(e) and 15d-15(e)) and internal control over financialreporting (as defined in Exchange Act Rules 13a-15(f) and 15d-15(f)) for theissuer and have:

a)                                      designedsuch disclosure controls and procedures, or caused such disclosure controls andprocedures to be designed under our supervision, to ensure that materialinformation relating to the issuer, including its consolidated subsidiaries, ismade known to us by others within those entities, particularly during theperiod in which this report is being prepared;

b)                                     designedsuch internal control over financial reporting, or caused such internal controlover financial reporting to be designed under our supervision, to providereasonable assurance regarding the reliability of financial reporting and thepreparation of financial statements for external purposes in accordance withgenerally accepted accounting principles;

c)                                      evaluatedthe effectiveness of the issuer’s disclosure controls and procedures andpresented in this report our conclusions about the effectiveness of thedisclosure controls and procedures, as of the end of the period covered by thisreport based on such evaluation; and

d)                                     disclosedin this report any change in the issuer’s internal control over financialreporting that occurred during the period covered by the annual report that hasmaterially affected, or is reasonably likely to materially affect, the issuer’sinternal control over financial reporting; and

5.               The issuer’s othercertifying officer and I have disclosed, based on our most recent evaluation ofinternal control over financial reporting, to the issuer’s auditors and theAudit Committee of the issuer’s Board of Directors (or persons performingthe equivalent functions):

a)                                      allsignificant deficiencies and material weaknesses in the design or operation ofinternal control over financial reporting which are reasonably likely toadversely affect the issuer’s ability to record, process, summarize and reportfinancial information; and

b)                                     anyfraud, whether or not material, that involves management or other employees whohave a significant role in the issuer’s internal control over financialreporting.

Dated: September19, 2007

David J. Mazzo

President and ChiefExecutive Officer

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